The present invention relates in general to door latches and more particularly relates to a door locking arrangement useful with appliance doors, especially the doors of so called self cleaning ovens to latch out the door during the high temperature cleaning operation.
Many kitchen and even commercial stoves now provide self-cleaning features which have heating means to generate very high temperatures within the oven during a cleaning cycle to pyrolytically decompose organic deposits on the surfaces of the oven. Such temperatures often exceed 380 degrees Fahrenheit.
The high temperatures involved in self-cleaning ovens can cause both personal and property damage if the oven is opened during the cleaning cycle. Accordingly, there is great interest in means to prevent opening the door during the high temperature cycle.
Some prior art ovens and the like which utilize self cleaning features have used a manual latch to be fastened when the self cleaning cycle is activated. In such systems a physical release is required to cause release of the door.
Such systems have the disadvantage that the door can still be inadvertently opened and so have required the development of means to to prevent the inadvertent opening of the door. In one case electrical means are provided generally where a solenoid or other such device is provided to be operated by a temperature system to lock the door latch when the oven is in the cleaning cycle.
In other cases temperature responsive bimetallic elements have been used to position pawl devices to prevent operation of the door release mechanism when the oven is in the cleaning cycle. Examples of such devices are shown in U.S. Pat. No. 3,438,666.
Additional such devices are shown in U.S. Pat. Nos. 3,540767 and 4,133,337.
However such systems suffer to some extent from time lag in both the heating and cooling periods leading to some liklihood of inadvertently opening the door during the heating cycle. U.S. Pat. No. 3,540,767 deals with this problem by limiting rotation of the bimetal strip.
However, temperature characteristics of ovens, even ovens from the same manufacturer vary widely and make it difficult to manufacture devices which fit all circumstances.
U.S. Pat. No. 4,862,870 teaches a snap action system using a pair of bimetal strips where one of the strips moves a locking pin to prevent release of the door latch mechanism while the second strip independently prevents movement of the locking pin until the second strip responds to lower temperature in the oven or chamber.
All of the prior art devices intended to accomplish the same or similar objectives as the present invention utilize complex multiple piece arrangements which, because of their complexity and number of individual cooperative elements, inherently have a high probability of failure relative to the straightforward assemblies permitted by the present invention.
No prior art arrangement is known which recognizes the benefits of the use of counterbalanced spring devices to lock a door latch mechanism where one of the springs is temperature responsive and overcomes the force exerted by another spring at selected temperature to lock the door release mechanism during periods of high temperature in the oven. Similar results are achieved by the use of gravity.